Passive optical networks (PONs) are a popular choice for modern communications systems. Both users and providers constantly demand increased performance for networks. Referring to FIG. 1, a diagram of a typical PON system, each of several optical line terminals (OLTs) 100 communicates with one or more optical network terminals (ONTs) 104. ONTs are also known as optical network units (ONUs). An OLT transmits over a downstream channel received by all ONUs, and assigns transmission slots on the upstream channel to specific ONUs. The bandwidth assignment may be static or dynamic based on real time traffic load at the specific ONUs and the ONUs' indicated needs for transmission bandwidth. A typical system consists of multiple OLT port controllers such as 105 in an OLT controller, such as OLT controller 102. Each OLT port controller, such as one of OLT port controllers 105, implements a respective OLT PON port, such as one of OLT PON ports 107, each PON port having an associated PON 108. Each OLT PON port is connected through a PON to multiple ONTs, such as ONTs 106. Each ONT provides services to one or more subscribers (end users). OLT PON ports are also referred to as PON ports, or PON channels. In the context of this document, the term PON system generally refers to all of the OLTs and related components associated with a given SNI.
Additional background information on PONs and related technology relevant to the current document can be found in the following specifications:                ITU-T Recommendation G.983—is a family of recommendations that defines broadband passive optical network (BPON) telecommunications access networks        ITU-T Recommendation G.984—is a family of recommendations that defines gigabit passive optical network (GPON) telecommunications access networks        ITU-T Recommendation G.987—is a family of recommendations that defines 10 gigabit passive optical network (XG-PON) telecommunications access networks        IEEE standard 802.3ah—Ethernet PON (EPON).        
PON systems typically require connectivity to a regional broadband network 120, also referred to as a metro network. A typical configuration is to connect multiple PONs 108 via associated OLT port controllers 105 and OLT controllers 102 to a regional broadband network through a common service network interface (SNI) 122. The SNI provides an uplink channel from the PON system to the regional broadband network 120. The location at which traffic is aggregated from OLT port controllers toward the SNI is known as an aggregation point 124. In the context of this document, traffic is also referred to as data. An aggregation device, such as an Ethernet switch 126, is typically used to aggregate traffic from the PON ports towards the SNI 122. Note that for clarity in FIG. 1 the direction of arrows show only the direction of traffic aggregation. One skilled in the art will realize that traffic flows are bi-directional, and that other connections between components in the PON system may exist for command, control, communications, and other system functions.
In most systems, the bandwidth capacity of the SNI uplink channel is much smaller (typically 2-10 times smaller) than the aggregated upstream bandwidth capacity of all the OLT PON channels. This condition is known also as “oversubscription”, and may result in network traffic congestion at the aggregation point. Network traffic congestion is highly undesirable, as congestion may result in increased traffic latency, loss of Quality-of-Service (QoS), and/or under-utilization of network resources.
Conventional PON systems may employ one of the following solutions in order to avoid congestion in the SNI uplink aggregation channel:                1. Priority based queuing in the aggregation switch. This technique protects high priority traffic and allows high priority traffic to flow even during congestion, however this technique will not resolve the congestion problem for equal priority traffic.        2. Limiting the rate of traffic of each PON channel. The aggregated traffic rate of all PON channels does not exceed the SNI bandwidth. This solution eliminates the congestion, but does not allow for dynamic allocation of bandwidth based on real time traffic demand conditions. As a result, the SNI bandwidth resources are not effectively utilized.        3. Using a dedicated traffic manager device. A traffic manager device, also referred to in the industry as simply a traffic manager, is a device that buffers ingress (upstream from ONTs) traffic, classifies the traffic into queues, and regulates the egress traffic (from the OLT port controllers towards the SNI) according to a configured service policy. Such a device solves the congestion problem, but traffic manager devices are very expensive compared to other system costs, and require additional resources (power, memory) in the system.        
There is therefore a need for congestion management solution in PON channels aggregation without using a dedicated traffic manager device and without static limiting of the traffic rate in each OLT.